This invention lies in the field of floppy disc drive systems and, in particular, of a disc drive with a direct rotational step motor drive. This invention also relates to stepper motor construction.
The floppy disc is now a widely accepted storage medium and, in particular, has become almost universally employed in office equipment and word processing devices. The floppy disc is a thin Mylar platter, either 8 inches in diameter in the standard size or 51/4 inches in diameter for the minifloppy. The smooth surface of the disc is coated with a magnetic oxide, and is housed in a square paper envelope having an opening or "window" through which the disc is exposed to the read-write head. Another smaller window provides access for detecting segment reference markings. The floppy disc can hold a substantial amount of information, i.e., a standard 8 inch disc is capable of holding a megabite. Associated with the floppy disc is a disc drive which is required to rotate the disc at a specific speed and to provide automated control of the read and write operations. Every apparatus which uses the floppy disc must necessarily have the associated floppy disc drive. The drives are necessarily relatively complex and have been relatively expensive. In view of this, and also in view of the projection for substantially increased use of floppy discs in the near future, it is important to provide an improved floppy disc drive which is simplified, less expensive, and is capable of being packaged in a smaller volume.
A floppy disc drive incorporating a rotary stepper motor drive is disclosed in copending application Ser. No. 56,987 filed July 12, 1979 now abandoned in favor of continuation application, Ser. No. 241,974, filed Mar. 9, 1981. A rotary stepper motor typically employs a plurality of pole positions symmetrically placed about the axis of the motor. Where efforts are made to reduce the overall height of the disc drive, the magnetic storage medium necessarily becomes more closely positioned to the magnetic fields which drive the motor. These magnetic fields create noise which can adversely affect the reading and writing of data on the magnetic storage medium.